Overvoltage protection device and manufacturing process for the same

ABSTRACT

An overvoltage protection device has a voltage-limiting region parallel to its central junction to produce a transverse junction breakdown. The spacing between the voltage-limiting region and the central junction defines the breakdown voltage. Via varying the size and location of the voltage-limiting region, the protection device can has various-breakdown voltages and lower breakover currents. Thereby, the sensitivity of the protection device can be improved.

FIELD OF THE INVENTION

The present invention is directed to an overvoltage protection deviceand manufacturing process for the same, and more particularly, to anovervoltage protection device having a voltage-limiting region disposedon a central contacting surface thereof for defining the breakdownvoltage and breakover current. Thereby, the present invention can makethe overvoltage protection device capable of adjusting the breakdownvoltage and breakover current.

BACKGROUND OF THE INVENTION

Recently, the manufacturing processes for electronic components are moreand more precise and their sizes also have become smaller and smaller.Hence, the devices used to protect electronic components from the damageresulting from electric effects, such as static electricity,overvoltage, electric arc and so on, also become more and moreimportant. For instance, the thyristor overvoltage protection devicesare used in the modern communication systems extensively. These devicesare used to protect the communication system from the damage resultingfrom lighting strikes on transmission lines, short circuits ofneighboring power lines or other unexpected events. These devices canprevent any damage resulting from the overvoltage effects.

The thyristor overvoltage protection device is a semiconductor devicedesigned to lead the overvoltage surge away from the transmission linebefore it reaches the communication system. Hence, it can be used toprotect the communication system. When the system operates regularly,this protection device is kept in a high-resistance status, i.e. in anoff status. At this moment, only the leakage current, which is lowerthan a microampere, can pass through this device. Hence, it won't affectthe operation of the whole system. When an overvoltage surge occurs onthe transmission lines, this device will switch to a low-resistancestatus, i.e. an on status. Thereby, this device can lead the overvoltagesurge away from the communication system. After the overvoltage surgepasses away, the overvoltage protection device will switch back to theoff status and the communication system will return to regularoperations.

The characteristics of the current and voltage of this overvoltageprotection device are shown in FIG. 1, which is a curve diagram of thevoltage (V) versus the current (I) of the conventional overvoltageprotection device.

In general, the thyristor overvoltage protection device has two metalelectrodes and a four-layer interleaving semiconductor structure, forexample, which is interleaved by NPNP-type or PNPN-type layers. The toplayer of this protection device is an emitter region, i.e. the cathoderegion; the second layer is a base region; the third layer is asubstrate region; and the fourth layer is an anode region. Therein, thetwo metal electrodes are disposed on the surfaces of the emitter regionand the anode region, respectively.

The junction between the base region and the substrate region is thecentral junction of this protection device. Under regular operation, thecentral junction will be reverse biased. When the reverse biasincreases, the central junction will breakdown. As shown in the figure,when the breakdown current reaches 1 mA, the voltage across theprotection device is defined as the breakdown voltage (Vz). If thevoltage increases constantly at this moment, the breakdown current willincrease rapidly and make the protection device switch to the on status.The voltage and current for making the protection switch to the onstatus are defined as the breakover voltage (VBO) and the breakovercurrent (IBO). When the overvoltage surge occurs and reaches thebreakover voltage (VBO), the overvoltage protection device will turn onto lead the induced current through the protection device and keep thevoltage across the protection device in a relatively low value. When theovervoltage surge passes away, the current passing through theprotection device will decrease constantly. When the current is lowerthan the holding current (IH) of the protection device, the overvoltageprotection device will switch back to the off status (as shown in thefigure) to make the voltage across the protection device return tonormal and make the communication system operate regularly.

Reference is made to FIG. 2, which is a schematic diagram of aovervoltage protection device disclosed in U.S. Pat. No. 4,967,256. Thethyristor overvoltage protection device has a four-layer semiconductorstructure (PNPN), including emitter regions 22 (n++), shorting dots 23disposed between the emitter regions 22, a substrate 20, a single buriedregion 25 (n) disposed inside the substrate 20, a base region 21 (p+),an anode region 24, a first metal electrode region 26 connected with theupper components, a second metal electrode region 27 connected with thelower components and a guard ring 28 (n++) surrounding the centraljunction. The guard ring 28 is used to make the potential difference ofthe component surface evenly distributed to improve the stability of thewhole device. Further, the guard ring 28 won't result in the breakdownof this semiconductor device.

As shown in FIG. 2, the buried region 25 and the substrate 20 both areN-type semiconductors, but the buried region 25 has a higher impurityconcentration. The breakdown voltage of the junction between the buriedregion 25 and the substrate 20 is lower than that between the baseregion 21 and the substrate 20. Hence, when the voltage across theprotection device increases, the breakdown effect will first occur atthe junction between the base region 21 and the buried region 25 andmake the breakdown current pass through the buried region 25 first. Thiseffect can improve the precision for controlling the breakdown voltageduring manufacturing process of the device. Further, it can make thisdevice have a breakover current even lower than that of the traditionaldevice without the buried region.

However, in application, this overvoltage protection device still hasdrawbacks. Since it employs a single buried region with relative smallsize, its conductivity will be limited during the on status. Hence, itwill cause a bottleneck effect, which will lower the current carryingcapacity of the device. In order to prevent the bottleneck effect, U.S.Pat. No. 5,001,537 and No. 5,516,705 disclose two kinds of overvoltageprotection devices employing multiple buried regions. However, since theoperation principle of the devices is still unchanged, i.e., asdescribed above, controlling the breakdown voltage and breakover currentvia employing the effect that the junction between the base region andthe buried region will breakdown first, which is different to thepresent invention.

Accordingly, the present invention disposes a voltage-limiting regionparallel to the central junction of the overvoltage protection deviceduring the manufacturing process of the semiconductor device fordefining the breakdown voltage and the breakover current of the device.Thereby, the present invention can provide a precise overvoltageprotection device. Since it doesn't have the buried region, it can havethe higher current carrying capacity.

SUMMARY OF THE INVENTION

An objective of the present invention is to provide an overvoltageprotection device and manufacturing process for the same. The presentinvention disposes a voltage-limiting region parallel to a centraljunction of the protection device to make the protection device able toproduce a transverse junction breakdown. The voltage-limiting region canbe used to define the breakdown voltage and breakover current of theprotection device. Via varying the size and location of thevoltage-limiting region, the sensitivity of the protection device forthe overvoltage surge can be improved considerably.

Furthermore, the manufacturing process of the present invention forms afirst shading layer on a substrate, etches the first shading layer toform a plurality of shading blocks to define a first region and a secondregion, forms the base region in the second region, forms thevoltage-limiting region in the first region; forms an emitter region onthe base region, and forms an electrode region on the emitter region.

Numerous additional features, benefits and details of the presentinvention are described in the detailed description, which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantages of thisinvention will be more readily appreciated as the same becomes betterunderstood by reference to the following detailed description, whentaken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a curve diagram of the voltage (V) versus the current (I) ofthe conventional overvoltage protection device;

FIG. 2 is a schematic diagram of a overvoltage protection devicedisclosed in U.S. Pat. No. 4,967,256;

FIG. 3 is a cross-sectional diagram of an overvoltage protection devicein accordance with the present invention;

FIG. 4 a is a top-view diagram of the first embodiment of theovervoltage protection device in accordance with the present invention;

FIG. 4 b is a top-view diagram of the second embodiment of theovervoltage protection device in accordance with the present invention;

FIG. 4 c is a top-view diagram of the third embodiment of theovervoltage protection device in accordance with the present invention;

FIG. 5 is a schematic diagram of a bi-directional overvoltage protectiondevice in accordance with the present invention; and

FIGS. 6 a-6 f illustrate a manufacturing process of the overvoltageprotection device in accordance with the present invention.

DETAILED DESCRIPTION

Reference is made to FIG. 3, which is a cross-sectional diagram of anovervoltage protection device in accordance with the present invention.As does the prior art, it also has a four-layer interleavingsemiconductor structure (PNPN). Therein, a P-type base region 32, whichhas a relatively high impurity concentration (p+), is disposed on anN-type substrate 30, which has a relatively low impurity concentration(n−). An anode region 32′ is disposed on the other side of the device.The base region 32 has emitter regions 34 disposed thereon. The emitterregions 34 have a high impurity concentration and have multiple emittershorting dots 35 formed therebetween. The PN junction between the baseregion 32 and the substrate 30 is the central junction of the protectiondevice.

The present invention further disposes a voltage-limiting region 33,which is shaped as a ring, a partial ring or segmented pieces and hashigher impurity concentration (n+), parallel to the central junction.Further, the protection device has a first electrode region 31 and asecond electrode region 31′ disposed on its upper and lower surfaces,respectively.

The voltage-limiting region 33 is made of an N-type semiconductor with arelatively high impurity concentration. Since its impurity concentrationis higher than that of the substrate 30, the transverse breakdownvoltage of the base region 32 is lower than the PN junction locatedbetween the lower portion of the base region 32 and the substrate 30.Hence, the breakdown voltage of the protection device is primarilydetermined according to the spacing between the base region 32 (p+) andthe voltage-limiting region 33. The larger the spacing is, the higherthe breakdown voltage is that can be obtained. Conversely, the smallerthe spacing is, the lower the breakdown voltage is that can be obtained.In practical application, the breakdown voltage can be changed viaadjusting the spacing between the voltage-limiting region 33 and thebase region 32 according to practical needs.

As shown in FIG. 3, the voltage-limiting region 33 is disposed on oneside of the base region 32. In practice, it is not limited. The totallength of the voltage-limiting region 33 can be used to determine thebreakover current of the overvoltage protection device. In other words,a breakdown region is formed between the voltage-limiting region 33 andthe base region 32 and the breakdown current can only pass through thisregion. When the breakdown phenomenon occurs, the total length of thevoltage-limiting region 33 will dominate the size of the breakdownregion and control the amount of the breakdown current passing throughthis breakdown region. Therein, if the length of the voltage-limitingregion 33 is short, the breakdown region will be small and the breakdowncurrent will be low. As shown in FIG. 1, when the protection device isswitched to the on status, the breakdown current is defined as thebreakover current (IBO) of the protection device. Hence, using thevoltage-limiting region 33 with short length can lower the breakovercurrent (IBO) effectively. Further, since the breakover current forswitching the protection device to on status is lowered, an overvoltageprotection device sensitive to the overvoltage can be obtained. Therein,the preferred embodiments are described as follows.

Reference is made to FIG. 4A, which is a top-view diagram of the firstembodiment of the overvoltage protection device in accordance with thepresent invention. The upper portion of the semiconductor substrate 30is surrounded by a circular voltage-limiting region 33 a made of anN-type semiconductor. There is a gap located between thevoltage-limiting region 33 a and the base region 32 made of a P-typesemiconductor. The emitter region 34 is disposed inside the base region32. The multiple holes shown in the figure are emitter shorting dots 35.The emitter region 34 has a first electrode region 31 disposed thereon.In general, the first electrode region 31 is a metal layer used toconnect with other components.

Reference is made to FIG. 4B, which is a top-view diagram of the secondembodiment of the overvoltage protection device in accordance with thepresent invention. The hatching 40 shown in this figure corresponds tothe cutaway view shown in FIG. 3. The components of the presentinvention can be modified according to the practical requirements.

Therein, the upper portion of the semiconductor substrate 30 issurrounded by a semicircular voltage-limiting region 33 b made of anN-type semiconductor. There is a gap located between thevoltage-limiting region 33 b and the base region 32 made of a P-typesemiconductor. The emitter region 34 is disposed inside the base region32 and has the multiple emitter shorting dots 35. The emitter region 34has the first electrode region 31 disposed thereon.

Reference is made to FIG. 4C, which is a top-view diagram of the thirdembodiment of the overvoltage protection device in accordance with thepresent invention. The hatching 40 shown in this figure corresponds tothe cutaway view shown in FIG. 3. The present invention can be modifiedaccording to the practical requirements.

Therein, the upper portion of the semiconductor substrate 30 issurrounded by a semicircular segmented voltage-limiting region 33 c madeof an N-type semiconductor. There is a gap located between thevoltage-limiting region 33 c and the base region 32 made of a P-typesemiconductor. The emitter region 34 is disposed inside the base region32 and has the multiple emitter shorting dots 35. The emitter region 34has the first electrode region 31 disposed thereon.

Taking FIG. 4C as an example, using segmented voltage-limiting regionnot only can reduce the total length of this voltage-limiting region butalso can equally distribute the breakdown phenomenon to a longer lengtharound the device. Hence, it can lower the breakover current andincrease the power dissipation capacity to increase the stability of thedevice.

Reference is made to FIG. 5, which is a schematic diagram of abi-directional overvoltage protection device in accordance with thepresent invention. Therein, the two opposed sides of the substrate 50both have a overvoltage protection device, including a first and secondbase regions 52 a, 52 b made of P-type semiconductors, a first andsecond voltage-limiting regions 53 a, 53 b disposed at the two sides, afirst and second emitter regions 54 a, 54 b respectively disposed on thebase regions, multiple first and second emitter shorting dots 55 a, 55 bformed inside the emitter regions, and a first and second electroderegions 51 a, 51 b disposed at the two surfaces of the device. Theovervoltage protection device shown in FIG. 3 is a uni-directionaldevice, which only has unidirectional overvoltage protection functions.However, the bi-directional overvoltage protection device shown in FIG.5 can provide bi-directional protection functions for the communicationsystems operated under alternative voltages.

Reference is made to FIGS. 6 a-f, which illustrate a manufacturingprocess of the overvoltage protection device in accordance with thepresent invention. This manufacturing process is used to produce theuni-directional protection device. As for the bi-directional ormulti-directional devices, they can also be produced according to thisprocess.

As shown in FIG. 6 a, a first shading layer 61 is formed on a substrate60 via oxidation or deposition process. The substrate 60 is mainly madeof silicon (Si) and the first shading layer 61 can be made of SiO2 orother membranous layer (e.g. Si3N4).

As shown in FIG. 6 b, via lithography and etching processes, the firstshading layer 61 can be etched to form the shading blocks 61 a, 61 b, 61c and multiple regions as shown in FIG. 6 b. Therein, the first region601, which will become the voltage-limiting region, is defined betweenthe shading blocks 61 a and 61 b. The second region 602, which willbecome the base region, is defined between the shading blocks 61 b and61 c. The width of the shading block 61 b is the spacing of the firstregion 601 (voltage-limiting region) and the second region 602 (baseregion) and used to determine the breakdown voltage value of thisdevice.

As shown in FIG. 6 c, a selected diffusion process or ion implantationprocess is used to diffuse or implant the impurity atoms into the secondregion 602 to form the base region 62 of the device, i.e. the P-typesemiconductor region shown in the figure.

As shown in FIG. 6 d, the selected diffusion process or ion implantationprocess is also used to diffuse or implant the impurity atoms into thefirst region 601 to form the voltage-limiting region 63 of the presentinvention.

As shown in FIG. 6 e, the selected diffusion process or ion implantationprocess is also used to diffuse or implant high-concentration impurityatoms into the base region 62 to form the high-concentration emitterregion 64 and the emitter shorting dots 65.

As shown in FIG. 6 f, finally, a metal layer is deposited on the emitterregion 64 as an electrode region 66 for electric conduction. And themanufacturing process of the protection device is ended at this step.

Furthermore, in FIG. 6 e mentioned above, the step for forming theemitter region can also be performed right after the base region isformed. The present invention is not limited to the manufacturing orderdescribed above. The steps described above can also be repeated orperformed simultaneously on the two sides of the substrate tomanufacture the bi-directional or multi-directional overvoltageprotection device.

The present invention disposes a voltage-limiting region parallel to thecentral junction of the overvoltage protection device. Via varying thesize and location of the voltage-limiting region, the present inventioncan define the breakdown voltage and breakover current so as to producean overvoltage protection device sensitive to the overvoltagephenomenon.

Although the present invention has been described with reference to thepreferred embodiment thereof, it will be understood that the inventionis not limited to the details thereof. Various substitutions andmodifications have been suggested in the foregoing description, andother will occur to those of ordinary skill in the art. Therefore, allsuch substitutions and modifications are embraced within the scope ofthe invention as defined in the appended claims.

1. A method for manufacturing an overvoltage protection device, whereina voltage-limiting region surrounds a base region of the overvoltageprotection device to control a breakdown voltage and a breakovercurrent, the method comprising: forming a first shading layer on asubstrate; etching the first shading layer to form a plurality ofshading blocks to define a first region and a second region; forming thebase region in the second region; forming the voltage-limiting region inthe first region; forming an emitter region on the base region; andforming an electrode region on the emitter region.
 2. The method asclaimed in claim 1, wherein the voltage-limiting region has a firstimpurity concentration larger than a second impurity concentration ofthe substrate.
 3. The method as claimed in claim 1, wherein thevoltage-limiting region and the base region produce a transversebreakdown phenomenon therebetween.
 4. The method as claimed in claim 1,wherein the breakdown voltage is defined according to a spacing betweenthe voltage-limiting region and the base region.
 5. The method asclaimed in claim 1, wherein the base region is completely or partiallysurrounded by the voltage-limiting region with a continuous shape or asegmented shape.
 6. The method as claimed in claim 1, wherein the stepfor forming the base region, the voltage-limiting region or emitterregion is performed via a diffusion process or an ion implantationprocess.
 7. The method as claimed in claim 1, wherein the substrate, thevoltage-limiting region or the emitter region is made of an N-typesemiconductor and the base region is made of a P-type semiconductor. 8.The method as claimed in claim 1, wherein the voltage-limiting region orthe emitter region is made of a P-type semiconductor and the base regionis made of an N-type semiconductor.
 9. The method as claimed in claim 1,wherein a structure of the overvoltage protection device is manufacturedrepeatedly to form a bi-directional or multi-directional overvoltageprotection device.
 10. An overvoltage protection device, comprising: asubstrate; a base region disposed on the substrate; a plurality ofemitter regions disposed on the base region; and a voltage-limitingregion disposed to surround the base region.
 11. The device as claimedin claim 10, where the substrate, the voltage-limiting region or theemitter region is made of an N-type semiconductor and the base region ismade of a P-type semiconductor.
 12. The device as claimed in claim 10,where wherein the voltage-limiting region or the emitter region is madeof a P-type semiconductor and the base region is made of an N-typesemiconductor.
 13. The device as claimed in claim 10, where thevoltage-limiting region has a first impurity concentration larger than asecond impurity concentration of the substrate.
 14. The device asclaimed in claim 10, where the overvoltage protection device is abi-directional or multi-directional overvoltage protection device. 15.The device as claimed in claim 10, where the base region is completelyor partially surrounded by the voltage-limiting region with a continuousshape or a segmented shape.